The invention relates to sampling tool to be immersed into a well for collection of samples during drilling for/production of oil, gas or water, and including a tubular, hollow and preferably cylindrical body.
During a drilling operation and during production of hydrocarbons it is necessary to collect samples of the gas/liquid present in a hydrocarbon reservoir. This is achieved by immersing into the well a sampling tool for collecting samples at different depths. The sampler is then hoisted to the surface where the sample is transferred from the sampling tool to a suitable transportation bottle for further laboratory analysis of the chemical and physical characteristics of the sample.
A sampling tool for obtaining gas-/liquid samples basically includes a tubular cylindrical body comprising a storage chamber for conversing the gas-/liquid samples taken and valves for opening and closing the inlets to the storage chamber. In addition to the storage chamber, the equipment also includes various electronic equipment for measuring pressure, temperature, etc. The sampling tool is connected to the surface by a lifting wire having an insulated copper core. The sampling tool may also be mechanically controlled from the surface by using a mechanical steering rod inside the pipe. The steering rod is used to open and close the valves for the supply of gas-/liquid samples.
Sampling tools with a storage chamber usually include a floating piston for separating the gas-/liquid sample physically from a counter pressure medium. The counter pressure medium is used to control the flow from the reservoir into the storage chamber. During sampling, the gas-/liquid samples flow into the chamber on one side of the piston and the counter pressure medium is pressed out of the cylinder into an atmospheric chamber. There are O-ring seals between the piston and the cylinder wall. These O-rings are exposed to wear caused by a combination of rubbing against the cylinder wall and contact with usually very aggressive hydrocarbon fluids. Besides, the seals allow diffusion from one side of the piston to the other. Therefore, the disadvantage of such tool is that hydrocarbons leak or diffuse from one side of the piston into the counter pressure medium on the other side of the piston. When fractions of the gas-/liquid sample diffuse or leak from the sample due to worn-out piston seals, the gas-/liquid sample will not be representative and the test has to be repeated. This increases the costs for obtaining oil- and gas samples considerably, especially offshore because of very expensive rig time.
Another method for sampling is to use tools with a time controlling system for opening the valves and a subsequent filling of the storage chamber. This method is not convenient, because problems or delays often arise when the equipment is brought down into the well. Both the time controlling system and the use of a steering rod for opening the valves depend on relatively complex mechanical systems. The mechanical systems as described are exposed to wear and defects which will lead to increasing expenses, both in the form of broken equipment and need for repeating the tests.